It has been recognized that the delivery of oxygen and oxygen-enriched air to the respiratory tract of a patient often results in discomfort to the patient, especially when the air is delivered over an extended period of time. It has also been recognized that the delivery of air having relatively low absolute humidity can result in respiratory irritation.
Several devices have been proposed to overcome these problems. U.S. Patent Publication No. 2003/0209246A1, the entire disclosure of which is incorporated herein by reference, describes embodiments of an apparatus and method for respiratory tract therapy adapted to heat and humidify air and to deliver heated and humidified air to the respiratory tract of a human patient. Devices such as those disclosed in U.S. Patent Publication No. 2003/0209246A1 represent an improvement over prior art devices.
Nevertheless, there remains a need for devices adapted to deliver supplemental breathing gases at low continuous flow rates such as flow rates less than about 5 liters per minute at high relative humidities such as about 100% relative humidity and in an elevated temperature range such as a temperature range from about 33° C. to about 43° C. There also remains a need for delivering gas warmed and humidified with water vapor at flow rates ranging from about 1 liter per minute or lower to about 8 liters per minute or higher.